Re: air pockets and false alarms (aka: Statistics)
All: I hope I am not misunderstanding the question. 1. Do wet systems using a pressure switch without integral retard installed at the top of a retard chamber generate unwanted alarms? The answer is definitely yes. The problem in the city I work for seems largely associated with systems with large internal volume. Flow switches and pressure switches as described both seem to have problems. But that may be result that the city I work in is characterized with distribution centers. Many have 0.39 gpm/sf over 5,600 sf. systems. Depending on the decade of installation, large tree, looped, or gridded systems. It also characterized by a large area without residences. Instead of many small water uses turn on and off, a fewer bigger industrial users turn water on and off. Use peaks in summers. Highest use is not 0500 to 0700 or 1700 to 1900 hrs. as most people, or at least me, guessed. Highest use is as 0200-0300 hrs. This non-intuitive use is landscaping irrigation sprinklers coming on. During this time another use that turns water on and off is parking lot washers. The pressures switches at top of retard chambers seem allowed by code; often within a few months of installation it is obvious they are problematic, and an alternative is used. Given the cost that is entailed by everyone concerned I fail to understand why if pressure swiches are to be use on a wet system, an integral retard are not always used. It costs to send a fitter out to correct the problem. (I always assume this is a call back the spk co. eats. Am I wrong - does the owner pay again?) 2. I've yet to see a prv on dry systems. It was my understanding the dry systems leak air, and that seasonally they bleed air excess air in the spring. The compressor just runs less. Is installing prv's a regional adaptation? Puget Sound is not known for blistering cold or blistering heat. My experience is all from here. 3. I've never seen the 300 psi on wet systems, and I've looked at a lot of guages. Those little 175 psi relief valves seem to be the most precise thing installed on a system. The bleed right to 175. 4. Jockey pumps. I want to make sure I am saying the same thing. I think of a jockey pump as a small pump of a few gpm in paralel with a big fire pump. The small pump runs to prevent the big pump from starting. Its start pressure is set above the start pressure for the big pumps controller. They use a real pump controller. Where fire pumps and jockey pumps are installed false alarm associated with pressure fluctuations are rare. They are usally corrected by sending the right person out to adjust controller settings. Most of our fire pumps are associated with ESFR pre-K25 heads. We have had a few customers who had to install excess pressure pumps at their systems. The problem was associated with normal pump runs causing false alarms. It also seems more of a problem with pumps serving a number of buidlings in industrial/distribution center campuses, as opposed to a just serving a single building. 5. Excess pressure pump. An excess pressure pump is again a small pump. It is not required to be listed for fire pump usage. It is normally 120 VAC. It's UL listing is just like my table lamp. The listing is for electrical safety, not functionality. It pumps from supply side of a (alarm usually) check valve to system side. (Please install the system connection above the flow switch.) They do not use a real fire pump controller. They maintain pressure in the system above that expected from pressure surges in the system. I've usually seen ~20 psi above observed system gauge prior to installation of pump. If the question is false alarms in wet sprinkler systems excess pressure pumps are a definitive solution. Once an excess pressure switch is installed our experience is that any further false alarms are associated with human communication difficulties, lightning activity Any thing but pressure fluctations. Yours, Bruce Verhei - Original Message - From: Ed Vining edvinin...@gmail.com To: sprinklerforum@firesprinkler.org Sent: Friday, March 20, 2009 11:38:15 AM GMT -08:00 US/Canada Pacific Subject: Re: air pockets and false alarms (aka: Statistics) Yes Jim. Pressure in the retard chamber is relieved through the drain when the alarm port is closed. On Fri, Mar 20, 2009 at 10:26 AM, jim.robe...@fluor.com wrote: I had not been following the thread because the subject title hasn't changed, but am I correct in assuming this problem does not occur with pressure switches at the top of retard chambers? James L.(Jim) Roberts, PE/SET Fluor Corporation 100 Fluor Daniel Drive - C104F Greenville, SC 29607 864.281.5149 864.281.4916(Fax) Jay Jay Blocker fire_sprinkler...@yahoo.com Sent by: sprinklerforum-boun...@firesprinkler.org 03/03/2009 08:09 PM Please respond to sprinklerforum To sprinklerforum@firesprinkler.org cc Subject Re:
Re: Excessive system pressure
Bill. Please don't do this without a pressure relief on a vessel. Or at least don't make the container that is solid use a liquified gas with a low boiling pressure. One ton Cl2 cylinders use very heavy walls. The ends are arched toward the product for security and strength. If you fail to leave a vapor space they bulge outward before the plugs fail. Not good. Bruce Verhei - Original Message - From: bill brooks bill.bro...@brooksfpe.com To: sprinklerforum@firesprinkler.org Sent: Friday, March 20, 2009 2:42:27 PM GMT -08:00 US/Canada Pacific Subject: RE: Excessive system pressure Rodney, You said you aren't hard headed and you understand the principles behind the system pressure increases. Here's a chance to prove both. 1. Two containers of identical volume. One container 50% water, the other container 100% water. Each has been sitting in a 50 F room with the lid off. In other words the liquid and the containers are at 50F. Now make sure the 100% container is topped off and put lids on both. Read the pressure gage and satisfy yourself they both read 0. Move both containers into a 120 F room and come back when the two systems reach 120 F. 2. Same as above, but remove 10% of the water from the filled container before capping and moving. When the systems reach 120 F, which container has the higher pressure in each of the cases above? Bill Brooks William N. Brooks, P.E. Brooks Fire Protection Engineering Inc. 372 Wilett Drive Severna Park, MD 21146 410-544-3620 Phone 410-544-3032 FAX 412-400-6528 Cell ___ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field) ___ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field)
RE: Excessive system pressure
Excellent information. So to summarize, it's agreed by all that excess pressure issues are valid and should be dealt with by way of valves or accessories designed for that application, such as PRV's. And alarm test connections can be located anywhere downstream of the device they're intended to test. Steve Leyton Protection Design Consulting San Diego, CA -Original Message- From: sprinklerforum-boun...@firesprinkler.org [mailto:sprinklerforum-boun...@firesprinkler.org] On Behalf Of Rodney Hamm Sent: Friday, March 20, 2009 9:13 AM To: sprinklerforum@firesprinkler.org Subject: RE: Excessive system pressure I FULLY INTEND THAT THIS WILL BE MY LAST POST REGARDING THIS SUBJECT. I promise to make a concerted effort to make this statement true. I would also like to state that you should probably read this entire post if you have not completely tuned out regarding this subject! I obtained my Bachelors Degree in Mechanical Engineering and I am also a FPE; I am fully aware and I understand thermal expansion. A few forum participants posted data regarding water, but refrained from including any thermal expansion data for air. My point is that thermal expansion effects both water and air. The following two paragraphs were copied from the internet: Charles's law states that when pressure is kept constant, there is a direct relationship between volume and temperature. As a gas heats up, its volume increases, and when it cools down, its volume reduces accordingly. Thus, if an air mattress is filled in an air-conditioned room, and the mattress is then taken to the beach on a hot day, the air inside will expand. Depending on how much its volume increases, the expansion of the hot air could cause the mattress to pop. That is to say, he discovered that if a container of air were to be sealed at 0*C, at ordinary atmospheric pressure of 15 pounds per square inch, and then heated to 100*C but kept at the same volume, the air would now exert a pressure of about 20 pounds per square inch on the sides of the container. (Of course, strictly speaking, the container will also have increased in size, that would lower the effect-but it's a tiny correction, about ½% for copper, even less for steel and glass.) Remarkably, if the air were initially at a pressure of thirty pounds per square inch at 0*C, on heating to 100*C the pressure would go to about 40 pounds per square inch-so the percentage increase in pressure was the same for any initial pressure: on heating through 100*C, the pressure would always increase by about 33%. Water on the other hand: On heating from 0*C through 30*C, the pressure will stay essentially constant, while heating from 30*C through 100*C, the pressure will increase by about 4%. Check out the thermal expansion properties of air and water if you think I am wrong. Web site: http://www.engineeringtoolbox.com/water-thermal-properties-d_162.html In summary, I guess I am simply trying to state that trapped air pockets will create a more significant pressure increase or decrease in a closed sprinkler system than water when the temperature changes. I will absolutely admit that I cannot explain mathematically why we see such drastic pressure increases in the numerous wet sprinkler systems where we have identified and resolved these issues (based strictly on Charles's Law, the pressure increases should not be so extreme), but I can state that the excessive pressure problem is completely resolved after we bleed off a significant amount of the trapped air pockets. This is not a theory, this is absolute real world action with undeniable results. Some systems relieve air for 20-40 minutes through multiple sprinkler heads (loosened enough to hear and feel the air escape from the system at the various high points). After we remove a significant amount of the trapped air, the problem is resolved. And to address the obvious question, the problem is resolved even without a 175 psi PRV (we do not always provide the 175 psi PRV, but we typically recommend them for gridded systems; some clients agree to provide them, but some decide against paying for the 175 psi PRV). I will officially let it go. I have planted a few seeds through this forum and hopefully caused a few people to think about the subject to some degree. I sincerely hope that I have not caused any animosity or hurt feelings..if so, PLEASE know that I had no intentions of making anyone feel bad in any way, shape or form. I also feel compelled to state that I am really not trying to win an argumentarguing or an obsession of being right is usually a fruitless and ultimately negative exercise. That being said, I imagine that I am now officially branded as argumentative and/or obsessive. I hope this is not the case, but I am a Big Boy and I can deal with it I guess! Over time, I sincerely hope everyone on this forum will realize that my overall intentions are to have a positive impact, learn from
Re: Excessive system pressure
A single example of very cold from several years ago when I used to work for a living. An unoccupied section of a warehouse. Wet sprinkle system. All the branch lines on that side of the riser end in that space. The heat has been turned off. Several freeze and break due to freezing. We can assume that there is no air trapped in the new ends of the broken lines since the ice plugs are keeping the system intact. There probably is trapped air at the other end and in the frozen end where branch lines have not broken. I'm called out because the riser is leaking around the flow switch. When I get there there is also water weeping out around all the face plate bolts. The gauge reads zero. As I'm standing in front of this riser I rap on the gauge a couple of time and get not wiggle in the needle. I look closer and the needle is pegged on the back side of the zeroing pin, ergo 300+ psi. Quick little dance to the side and I try to open the main drain to bleed this sucker off. No chance even though my personal little hell there is literally frozen over. I finally cracked the main drain using a Texas Ten (ten-inch pipe wrench with a cheater that extends the handle to the same leverage as an 18 wrench) on the stem. I felt like I was in one of those submarine movies where flange bolts are going to start shooting off. The power ice. So question of the day: If thermal expansion causes pressure to rise/fluid to expand when heat is applied and to contract when heat is removed what then causes water to also expand when it reaches it's freezing point and is this true for all fluids. This two-part question is worth 50% of your final exam relative to this thread. And Rodney, thanks for your final comments. I for one was thinking you were being more than a little contentious, arrogant and argumentative (in the negative context of that word), but after stating your intent throughout the thread all is forgiven. As in all institutions the Forum has a culture and sometimes it takes a new guy a bit of time to settle in. John Drucker can probably remember this crazy guy that entered the alarm forum, pretty much told everyone they were idiots, and at one point attacked me with a verbal violence I reserve for Hitler his ilk because he took some offense at a joking comment I made to another member thinking I was insulting him. I offered a left-handed apology which he accepted, missing the sarcasm, and eventually left the forum. You seem to have gotten the culture here right, so welcome. On Sun, Mar 22, 2009 at 10:11 AM, Steve Leyton st...@protectiondesign.com wrote: Excellent information. So to summarize, it's agreed by all that excess pressure issues are valid and should be dealt with by way of valves or accessories designed for that application, such as PRV's. And alarm test connections can be located anywhere downstream of the device they're intended to test. Steve Leyton Protection Design Consulting San Diego, CA -Original Message- From: sprinklerforum-boun...@firesprinkler.org [mailto:sprinklerforum-boun...@firesprinkler.org] On Behalf Of Rodney Hamm Sent: Friday, March 20, 2009 9:13 AM To: sprinklerforum@firesprinkler.org Subject: RE: Excessive system pressure I FULLY INTEND THAT THIS WILL BE MY LAST POST REGARDING THIS SUBJECT. I promise to make a concerted effort to make this statement true. I would also like to state that you should probably read this entire post if you have not completely tuned out regarding this subject! I obtained my Bachelors Degree in Mechanical Engineering and I am also a FPE; I am fully aware and I understand thermal expansion. A few forum participants posted data regarding water, but refrained from including any thermal expansion data for air. My point is that thermal expansion effects both water and air. The following two paragraphs were copied from the internet: Charles's law states that when pressure is kept constant, there is a direct relationship between volume and temperature. As a gas heats up, its volume increases, and when it cools down, its volume reduces accordingly. Thus, if an air mattress is filled in an air-conditioned room, and the mattress is then taken to the beach on a hot day, the air inside will expand. Depending on how much its volume increases, the expansion of the hot air could cause the mattress to pop. That is to say, he discovered that if a container of air were to be sealed at 0*C, at ordinary atmospheric pressure of 15 pounds per square inch, and then heated to 100*C but kept at the same volume, the air would now exert a pressure of about 20 pounds per square inch on the sides of the container. (Of course, strictly speaking, the container will also have increased in size, that would lower the effect-but it's a tiny correction, about ½% for copper, even less for steel and glass.) Remarkably, if the air were initially at a pressure of thirty pounds per square inch at 0*C, on heating to 100*C the
Excessive system pressure
So question of the day: If thermal expansion causes pressure to rise/fluid to expand when heat is applied and to contract when heat is removed what then causes water to also expand when it reaches it's freezing point and is this true for all fluids. This two-part question is worth 50% of your final exam relative to this thread. my guess is--- what causes water to expand when it freezes has to do with the way the molecular lattice forms in the solid phase. The little buggers don't hug so tightly, when they realize they are stuck with their nearest neighbor from now until...well...until their personal hell thaws over. no, it is not true for all fluids. water being one of the few molecules that behaves in this way. If it did not behave in this way, it would be SHTF time. we would not be here. that is because our planet would have frozen over long ago. when liquid water expands to form solid ice, it becomes less dense than liquid--- which is nice. nice because it insulates the water below, so the fish can continue to go about their business. if ice were denser than liquid water, ice would sink, allowing the surface to continue to generate more and more ice, probably leading to a solid frozen slab of water through its thickness. not good for aquatic life, which is not good for terrestial life, either. scot deal excelsior fire engineering ___ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field)
Re: Excessive system pressure
It is hard to remember all the ways that water is a special chemical. Bruce Verhei no, it is not true for all fluids. water being one of the few molecules that behaves in this way. scot deal excelsior fire engineering ___ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field) ___ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field)
Re: air pockets and false alarms (aka: Statistics)
James, I would have to answer No to your question. In my experience, the problem is typically much more common with retard chambers which are equipped with pressure switches. I stated this in one of my previous emails, but you are the first person I have noticed who asked specifically about retard chambers with pressure switches. The problem usually shows itself the night after the system has been drained/filled or tested (i.e. main drain tests or ITC testing) or within a week or two if the daytime and nighttime temperatures are not drastically different. The false alarm problem exists if the air pockets are large enough OR if the public water supply has a normal cycle which results in higher city main pressures at night than during the day (primarily when they fill the gravity tanks). I have seen this problem many times at facilities fed by the public water supply as well as facilities fed by fire pumps with jockey pumps. As the air pocket volume decreases due to colder temperatures at night, water enters the system piping. During small fluctuations water enters the system through the bypass line or ball check in the clapper (if provided) with no false alarm. During larger pressure fluctuations, the clapper opens slightly to accommodate the slightly larger water flow rate; usually just enough to fill the retard chamber and activate the pressure switch (10-25 seconds is usually all that is needed for most retard chambers). I have noticed these false alarms are also more common when a cold front moves through which has rain (I suppose the building temperature drops faster in this situation). Pressure switches on retard chambers do not have delay settings and typically activate sooner/quicker than a flow switch set with a 30-60 second delay. The problem sometimes remains idle after the low temperatures have allowed enough water to enter the system and the air pockets have been compressed enough to maintain a system pressure higher than the public water supply UNTIL the next drastic temperature drop and even colder cold front moves through. This is when the plant maintenance man closes the alarm line for good because he knows just enough to realize this action will permanently resolve the problem (if he did not already do it immediately following the first false alarm!). Fire alarm system is no longer active, but the false fire alarm issue is no longer a problem. Am I really the only person in America who has seen this scenario? If anyone else has experienced this problem, please send a quick email and let us all know what you did to resolve the issue. Ant doubters reading this email should probably ask themselves a question. How many times have you visited a facility and found the alarm line for the water motor gong closed? This is a fairly good indication they have had false alarms; if you ask the right people at the facility, they will probably remember since false fire alarms are very aggravating to them. My brother is a Lieutenant on a local fire department and they get called on false fire alarms on a very regular basis. If you encounter this problem and want to be completely sure this is the culprit, my advice is to place a 5 gallon bucket to catch the water in the retard chamber drain line. If you have a false alarm and the bucket has water, this is probably what happened. I usually cover the top of the bucket with plastic to prevent rain water accumulation. I have done this several times to prove to my customers that the problem is not with the electronic components in the alarm system. One customer actually sealed the alarm test valve, alarm line valve, main drain and ITC to make completely sure nobody was opening the valves at night; I really liked the idea. In these instances, the easiest resolution might be to remove the pressure switch and provide a flow switch which allows for a longer delay depending, of course, on how long water flows into the system during the false alarm events. I usually install the flow switch and remove as much air as possible when I reinstate the system and the problem is exterminated! Take care, Rodney K. Hamm, P.E. President/Owner Falcon Fire Protection Office (478) 953-1677 Cell (478) 396-6988 Date: Fri, 20 Mar 2009 13:26:59 -0400 From: jim.robe...@fluor.com Subject: Re: air pockets and false alarms (aka: Statistics) To: sprinklerforum@firesprinkler.org Message-ID: ofe5d18c54.116385b3-on8525756f.0044b35b-8525757f.005ff...@fluor.com Content-Type: text/plain; charset=us-ascii I had not been following the thread because the subject title hasn't changed, but am I correct in assuming this problem does not occur with pressure switches at the top of retard chambers? James L.(Jim) Roberts, PE/SET Fluor Corporation 100 Fluor Daniel Drive - C104F Greenville, SC 29607 864.281.5149 864.281.4916(Fax) ___ Sprinklerforum mailing list
Re: Excessive system pressure
Michael, Thanks for posting an accurate compression constant for liquid water. I should have known better than to grab something from the internet for a quick post (1 part in 5x10^7). Nothing like being off by a few orders of magnitude! I've since found a decent site on water, if you're curious: http://www.lsbu.ac.uk/water/explan2.html Take care and God bless. Michael Fitz wrote: Rodney, I deal with these problems all the time. The sprinkler system MUST have some air in it or an expansion tank otherwise the pressure will jack up to high pressures. We see this problem every time a check valve is installed in a domestic water system where there is a water heater downstream. Cold water fills the system and is then heated, say from 50 to 130. The volumetric expansion of water is very high when compared to the linear expansion of the copper water pipes (or the steel pipes of a sprinkler system) and the water will drain out of the PRV. If it doesn't have one, something breaks as explained below. As with most real systems, it can be extremely complicated to exactly model and calculate precisely what happens. Assume that water expands when heated, albeit a small amount. This amount is about .000207/degree C at 68F. For a 1% change in volume and assuming the factor is constant (it isn't), we would need to heat the water 48 degrees C or about 87 F. Also assume that water is somewhat compressible. Table 5.4 of Eshbach's Handbook of Engineering Fundamentals, 4th Edition, lists the compressibility (K or Beta) of water at 68F as 318,000 PSI where dP=dV*K This means for a 1% change in volume, the pressure would go up or down 3,180 PSI. IF we assume a completely sealed rigid container full of water, not too unlike a sprinkler system, then we just need to equate the thermal expansion of water to the compressibility of water. This way, the change in volume cancels out. In other words, if we heated the water 87F, then the pressure would rise 3,180 PSI. This rough calculation indicates that the pressure would theoretically increase about 36 PSI per degree F. Now in real life, the pipes also expand because of the temperature rise (2X the linear expansion rate) AND because the pressure rise of the water stresses the material so it also elastically expands. If there are any gaskets that allow the pipes to move a little in the groove, that changes things a little. So you can see the actual pressure rise is difficult to calculate but what happens is that the actual pressure rise in a system is a lot less than that rigid container calculation shown above. This is how we select expansion tanks, see http://www.watts.com/pro/divisions/watersafety_flowcontrol/learnabout/learna bout_thermexpansion.asp It's a good explanation why it is so very dangerous to overfill a propane tank. The liquid will expand until the tank goes hydraulic and then it burps over the PRV with a very little change in temperature. General rules of thumb: Water compressibility 318,000 PSI, Glycerin = 630,000 PSI. Glycerin can exert twice the force assuming the same temperature change, another reason to have the right expansion tanks on an antifreeze system. Air (assuming ideal) P2 = P1*V1/V2. Halve the volume, double the absolute pressure, quite compressible. P2 = P1*T2/T1 Double the absolute temperature and you double the absolute pressure. As an example, for a temperature rise of air in a rigid container from 68F to 98F and a system pressure of 75 PSIA, the pressure would increase to 75*(98+460)/(68+460) or 79.3 PSIA. For those that read gauges, essentially from 60 to 64 PSI. Hope this clears up why trapped air pockets DON'T cause significant pressure increases with temperature and why air free systems dangerously increase in pressure with rises in temperature. Michael Michael M. Fitz, P.E., C.F.I. MDE Inc. 700 S. Industrial Way Seattle, WA 98108 www.MDE.com 206-321-1804 ___ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field)
Southwest Airlines FALSE advertisment
Hello sprinklerforum, Has anybody else seen the TV commercial where the guy has something in the microwave, The microwave emits a shower of sparks and the sprinklers in the room go off? I looked at their website for an email address to write to, but all they have is a feedback form... Anybody in Dallas want to track down an email address for Gary Kelly ? I called customer service and they said they did not have it. Thanks -- Best regards, Charles Thurston Coastal Fire Protection mailto:coastalf...@sc.rr.com ___ Sprinklerforum mailing list http://lists.firesprinkler.org/mailman/listinfo/sprinklerforum For Technical Assistance, send an email to: techsupp...@firesprinkler.org To Unsubscribe, send an email to:sprinklerforum-requ...@firesprinkler.org (Put the word unsubscribe in the subject field)
